Delta iron

Allotropic modification of iron, also referred to as δ-ferrite (δ solid solution).

At normal temperature, iron has a body-centered cubic lattice. This ferrite phase at normal temperature is referred to as alpha-iron (Fig. 1a). However, α-iron is not stable at all temperature levels. Above 911 °C the body-centered phase transfers to the cubic face-centered γ-phase (Fig. 1b). This modification, referred to as austenite is stable up to a temperature of 1392 °C, then, it transfers back again to body-centered α-phase that melts and solidifies at 1536 °C (Fig. 2).


  • Figure 1: a) Elementary cell of cubic body-centered α-iron, b) Elementary cell of cubic face-centered γ-iron
  • Fig. 2: Cooling curve of pure iron